Populations irradiated in the course of medical, occupational, environmental, or military circumstances are being studied to quantify cancer risks and to learn more about carcinogenic mechanisms. When possible, laboratory studies are incorporated into epidemiologic investigations. Staff members serve on committees advising the government and international agencies. Recent findings indicate that (1) systemic chemotherapy combined with radiotherapy greatly enhances the risk of leukemia in women treated for breast cancer; (2) radiotherapy for breast cancer also increases the risk of cancer in the opposite breast, but only among women under the age of 45 when treated; (3) radiotherapy for peptic ulcer increases the risk of stomach cancer, which is further increased after surgical treatment; (4) adult survivors of childhood retinoblastoma continue to be at high risk for developing a second cancer; radiotherapy enhances the genetic susceptibility for osteosarcoma; (5) high doses at high dose rates are less leukemogenic than low doses at low dose rates among women treated for cancer of the endometrium; (6) diagnostic doses of radioactive iodine did not increase the risk of thyroid cancer, suggesting that protraction of dose reduces risk; (7) twins are at significantly low risk of developing childhood cancer than single births despite being exposed more frequently to prenatal x-rays; (8) indoor exposure to radon appears less hazardous than previously thought; (9) the risk of lung cancer among underground miners increases with cumulative exposure to radon and decreases with attained age and time since exposure; (10) among A-bomb survivors, early age at first time pregnancy protected against radiation-induced breast cancer; (11) radiation-induced thyroid cancer is not apparent among those exposed after age 20; (12) non-melanoma skin and liver cancers were linked to A-bomb irradiation for the first time; (13) in both A-bomb survivors and uranium miners, radiation-induced lung cancers tend to be of the small-cell subtype.